Ominous silence

Research shows that the worse the hearing loss, the greater the risk of developing dementia - but the jury is out on whether hearing aids can make a difference, writes Katherine Bouton.

At a party the other night, I found myself in conversation with a well-known author whose work I greatly admire. I use the term ''conversation'' loosely. I couldn't hear a word he said. But, worse, the effort I was making to hear was using up so much brainpower I completely forgot the titles of his books.

A senior moment? Maybe. (I'm 65.) But, for me, it is complicated by the fact that I have severe hearing loss, only somewhat eased by a hearing aid and cochlear implant.

Dr. Frank Lin, an otolaryngologist and epidemiologist at the Johns Hopkins School of Medicine, describes this phenomenon as ''cognitive load''. Cognitive overload is the way it feels. Essentially, the brain is so preoccupied with translating the sounds into words that it seems to have no processing power left to search through the store rooms of memory for a response.

Over the past few years, Lin has delivered unwelcome news to those of us with hearing loss. His work looks ''at the interface of hearing loss, gerontology and public health'', he writes on his website. The most significant issue is the link between hearing loss and dementia.

In a 2011 paper in Archives of Neurology, Lin and colleagues found a strong association between the two. The researchers looked at 639 people who were part of the Baltimore Longitudinal Study of Ageing. None had cognitive impairment at the beginning of the study, which followed subjects for 18 years, some had hearing loss.

''Compared to individuals with normal hearing, those individuals with a mild, moderate and severe hearing loss, respectively, had a two, three and fivefold increased risk of developing dementia over the course of the study,'' Lin says. The worse the hearing loss, the greater the risk of developing dementia.

The correlation remained true even when age, diabetes and hypertension - other conditions associated with dementia - were ruled out.

In an interview, Lin discussed some possible explanations for the association. The first is social isolation, which may come with hearing loss, a known risk factor for dementia. Another possibility is cognitive load and a third is some pathological process that causes hearing loss and dementia.

In a study last month, Lin and colleagues looked at 1984 older adults beginning in 1997-98, again using a well-established database. Their findings reinforced those of the 2011 study but also found that those with hearing loss had a ''30 to 40 per cent faster rate of loss of thinking and memory abilities'' during a six-year period compared with people with normal hearing. Again, the worse the hearing loss, the worse the rate of cognitive decline.

Both studies also found, somewhat surprisingly, that hearing aids were ''not significantly associated with lower risk'' for cognitive impairment. But self-reporting of hearing aid use is unreliable and Lin's next study will focus specifically on the way hearing aids are used.

In a recent paper in the journal Neurology, Dr John Gallacher and colleagues at Cardiff University suggested the possibility of a genetic or environmental factor that could be causing both hearing loss and dementia - and perhaps not in that order. In a phenomenon called reverse causation, a degenerative pathology that leads to early dementia might prove to be a cause of hearing loss.

The work of John Cacioppo, the director of the social neuroscience laboratory at the University of Chicago, also offers a clue to a pathological link. His multidisciplinary studies on isolation have shown that perceived isolation, or loneliness, is ''a more important predictor of a variety of adverse health outcomes than is objective social isolation''. Those with hearing loss, who may sit through a dinner party and not hear a word, frequently experience perceived isolation.

Other research, including the Framingham Heart Study, has found an association between hearing loss and another unexpected condition: cardiovascular disease. Again, the evidence suggests a common pathological cause. Dr David Friedland, a professor of otolaryngology at the Medical College of Wisconsin in Madison, hypothesised in a 2009 paper delivered at a conference that low-frequency loss could be an early indication that a patient has vascular problems. The inner ear is ''so sensitive to blood flow'' that any vascular abnormalities ''could be noted earlier here than in other parts of the body''.

A common pathological cause might help explain why hearing aids do not seem to reduce the risk of dementia. But those of us with hearing loss hope that is not the case.

A critical factor may be the way hearing aids are used. A user must practise to maximise their effectiveness and they may need reprogramming by an audiologist. Additional assistive technologies like looping and FM systems may also be required. And people with progressive hearing loss may need new aids every few years.

In one study, Lin and a colleague, Dr Wade Chien, found that only one in seven adults who could benefit from hearing aids used them.

Hearing loss is a natural part of ageing. But, for most people with hearing loss, according to the National Institute on Deafness and Other Communication Disorders, the condition begins long before they get old. Almost two-thirds of men with hearing loss began to lose their hearing before age 44. My hearing loss began when I was 30.

Forty-eight million Americans suffer from some degree of hearing loss. In Australia, one in six people has some degree of hearing loss, which is expected to rise to one in four by 2050.

If it can be proved in a clinical trial that hearing aids help delay or offset dementia, the benefits would be immeasurable.

The New York Times

Adapted from Shouting Won't Help: Why I - and 50 million Other Americans - Can't Hear You by Katherine Bouton.